Device and method for metering a reducing agent into an exhaust gas system of a motor vehicle

Abstract

In an internal-combustion engine exhaust gas system, a storage tank stores the reducing agent, a supply pipe connects the storage tank to a metering unit which introduces the reducing agent into the exhaust gas system. A pump mechanism within the supply pipe conveys the reducing agent. A pressure sensor detects the pressure in the supply pipe downstream of the pump, and a pressure-releasing device has a return pipe connected to the storage tank and comes off the supply pipe. A first valve system is arranged in the supply pipe. A section of the return pipe is located at a higher level than the return pipe to form a storage volume for air present in the supply pipe. A second valve system is arranged in the supply pipe to create, when the second valve system is closed, a storage volume for pressurized reducing agent by way of this pipe branch.

What is claimed is: 
     
       1. A system for introducing a reducing agent into an exhaust gas stream of an internal-combustion engine, the system comprising:
 a storage tank for storing the reducing agent, 
 a pump in fluid communication with the storage tank operable to draw the reducing agent from the storage tank and deliver it to a supply pipe, 
 a metering valve dispensing the reducing agent directly into the exhaust gas stream from the supply pipe, 
 a pressure sensor for detecting the pressure in the supply pipe downstream of the pump, 
 a temperature sensor measuring a temperature at a point in the system, 
 a return pipe having two ends, one end connected to the top of the storage tank and the other end coming off at a branch of the supply pipe downstream of the pump and upstream of the metering valve, 
 a first electrically controllable valve arranged in the return pipe, 
 wherein a section of the return pipe located between the branch and entry of the first electrically controllable valve is located at a higher level than the supply pipe, thereby forming a storage volume for air present in the supply pipe, and 
 a second electrically controllable valve arranged in the supply pipe downstream of the branch and upstream of the metering valve, the section of the supply pipe which is located between the branch and entry of the second electrically controllable valve being shorter than the section of the supply pipe between the exit of the second electrically controllable valve and the metering valve, and 
 a controller configured to: 
 in response to detecting a temperature below a predefined temperature threshold, automatically open the first electrically controllable valve and close the second electrically controllable valve if the internal-combustion engine is shut off and maintain said opening and closing of the first and second electrically controllable valves to provide circular pumping of the reducing agent through the storage tank until the detected temperature exceeds the predefined temperature threshold, 
 in response to detecting a pressure below a predefined minimum pressure threshold value, automatically close the second electrically controllable valve and open the first electrically controllable valve and the metering valve, such that with the second electrically controllable valve closed by the controller and the first electrically controllable valve and the metering valve are opened by the controller:
 (a) air present in the supply pipe upstream of the second electrically controllable valve vents into the top of the storage tank via the open first electrically controllable valve and the return line, and 
 (b) the metering valve injects a volume of reducing agent present in the section of the supply pipe between the exit of the second electrically controllable valve and the metering valve. 
 
 
     
     
       2. The system according to  claim 1 , wherein the reducing agent comprises a urea solution or an ammonia solution. 
     
     
       3. The system according to  claim 1 , wherein the pump comprises a diaphragm pump. 
     
     
       4. The system according to  claim 1 , further comprising a filter configured to remove impurities from the reducing agent disposed in the supply pipe. 
     
     
       5. A method for introducing a reducing agent into an exhaust gas stream of an internal-combustion engine with a storage tank for storing the reducing agent, a pump in fluid communication with the storage tank operable to draw the reducing agent from the storage tank and deliver it to a supply pipe, a metering valve dispensing the reducing agent directly into the exhaust gas stream from the supply pipe, a pressure sensor for detecting the pressure in the supply pipe downstream of the pump, a return pipe connected to the top of the storage tank and coming off at a branch of the supply pipe downstream of the pump and upstream of the metering valve, and a first electrically controllable valve arranged in the return pipe, the method comprising:
 closing the first electrically controllable valve, 
 injecting the reducing agent into the exhaust stream while the first electrically controllable valve restricts flow into the return pipe connected back to the top of the storage tank, 
 continually comparing pressure values detected by the pressure sensor with a predefined minimum pressure threshold value, 
 detecting one or more pressure values that fall below the predefined minimum pressure threshold value, 
 detecting a temperature of the reducing agent at a point in the system, and 
 in response to detecting one or more pressure values that fall below the predefined minimum pressure threshold value:
 automatically closing a second electrically controllable valve arranged in the supply pipe downstream of the branch and upstream of the metering valve, thereby causing air present in the supply pipe upstream of the second electrically controllable valve to collect in a section of the return pipe between the branch and entry of the first electrically controllable valve and located at a higher level than the supply pipe, the section serving as a storage volume, and 
 with the second electrically controllable valve closed, controlling the metering valve to inject a volume of reducing agent present in a section of the supply pipe between an exit of the second electrically controllable valve and the metering valve, and 
 
 in response to the detected temperature below a predefined temperature threshold, automatically opening the first electrically controllable valve and closing the second electrically controllable valve if the internal-combustion engine is shut off and maintaining said opening and closing of the first and second electrically controllable valves to provide circular pumping of the reducing agent through the storage tank until the detected temperature exceeds the predefined temperature threshold. 
 
     
     
       6. The method according to  claim 5 , further comprising, after closing of the second electrically controllable valve, supplying pressurized reducing agent at least intermittently to the metering valve from the section of the supply pipe located downstream of the second electrically controllable valve and serving as the storage volume. 
     
     
       7. The method according to  claim 6 , further comprising, after closing of the second electrically controllable valve for after a predetermined period opening of the first electrically controllable valve, thereby causing the air that has collected in the pipe section to flow back into the storage tank via the return pipe. 
     
     
       8. A method for introducing a reducing agent into an exhaust gas stream of an internal-combustion engine with a storage tank for storing the reducing agent, an electrical pump in fluid communication with the storage tank operable to draw the reducing agent from the storage tank and deliver it to a supply pipe, a metering valve injecting the reducing agent directly into the exhaust gas stream from the supply pipe, a return pipe connected to the top of the storage tank and coming off at a branch of the supply pipe downstream of the electrical pump and upstream of the metering valve, and a first electrically controllable valve arranged in the return pipe, the method comprising:
 closing the first electrically controllable valve, 
 injecting the reducing agent into the exhaust stream while the first electrically controllable valve restricts flow into the return pipe connected back to the top of the storage tank, 
 detecting values of an electrical current consumed by the pump using a current detector and continually comparing the detected electrical current values with a predefined minimum current threshold value, 
 detecting one or more electrical current values that fall below the predefined minimum current threshold value, 
 detecting a temperature of the reducing agent at a point in the system, and 
 in response to detecting one or more electrical current values that fall below the predefined minimum current threshold value:
 automatically closing a second electrically controllable valve arranged in the supply pipe downstream of the branch and upstream of the metering valve, thereby causing air present in the supply pipe upstream of the second electrically controllable valve to collect in a section of the return pipe located between the branch and entry of the first electrically controllable valve and at a higher level than the supply pipe, the section serving as a storage volume, and 
 with the second electrically controllable valve closed, controlling the metering valve to inject a volume of reducing agent present in a section of the supply pipe between an exit of the second electrically controllable valve and the metering valve, and 
 
 in response to the detected temperature below a predefined temperature threshold, automatically opening the first electrically controllable valve and closing the second electrically controllable valve if the internal-combustion engine is shut off and maintaining said opening and closing of the first and second electrically controllable valves to provide circular pumping of the reducing agent through the storage tank until the detected temperature exceeds the predefined temperature threshold. 
 
     
     
       9. The method according to  claim 8 , further comprising, after closing of the second electrically controllable valve, supplying pressurized reducing agent at least intermittently to the metering valve from the section of the supply pipe located downstream of the second electrically controllable valve and serving as the storage volume. 
     
     
       10. The method according to  claim 8 , further comprising, after closing of the second electrically controllable valve for after a predetermined period opening the valve of the first electrically controllable valve, thereby causing the air that has collected in the pipe section to flow back into the storage tank via the return pipe.